10. The Intestines Flashcards
What two routes can electrolytes, water and nutrients take from the gut lumen into the blood?
Cellular and paracellular.
What 3 things result in the large surface area of the intestines to aid absorption?
Mucosa folded into villi, surface is covered with microvilli (brush boarder) and intestine has plicae circulares.
In what form can carbohydrates be absorbed?
As monosaccharides.
Where does the final breakdown of carbohydrates into monosaccharides occur and by what enzymes?
In the brush boarder by brush boarder enzymes.
What ion is required for glucose to enter the brush boarder of the intestines?
Na+.
Name 2 monosaccharides
Fructose.
Galactose.
Glucose.
Name 2 common dietary carbohydrates
Starch (polysaccharide).
Lactose (disaccharide).
Sucrose (disaccharide).
What are the two components of starch, and what type of bonds are found between each?
Amylose - alpha-1-4 bonds.
Amylopectin - alpha-1-4 bonds between horizontal chains, and alpha-1-6 bonds vertically between every two glucose (one maltose) molecules.
What bonds does amylase break in starch digestion?
Alpha-1-4 bonds between glucose molecules in amylose.
What is a common breakdown product of starch?
Maltose (two glucose molecules).
What bonds does alpha dextrin break in starch digestion?
Alpha-1-4 bonds in amylopectin.
What bonds does isomaltase break in starch digestion?
Alpha-1-6 bonds in amylopectin.
With what brush boarder enzymes are the following products from initial starch digestion broken down into glucose:
Maltose?
Alpha dextrin?
Maltose - maltase.
Alpha dextrins - isomaltase.
With what brush boarder enzymes are lactose and sucrose broken down, and into what?
Lactose - with lactase into glucose and galactose.
Sucrose - with sucrose into glucose and fructose.
How is glucose absorbed by an enterocyte?
The Na+/K+ ATPase on the basolateral membrane maintains the low intracellular [Na+] by moving Na+ into the capillaries.
SGLT-1 binds Na+, which then allows glucose binding, and Na+ and glucose moves into the cell.
GLUT2 transports glucose out of the enterocyte, as glucose diffuses down its concentration gradient into the capillary blood.
Fructose uses a different transporter to glucose to enter into the enterocyte. What transporter does it use?
GLUT5.
How do oral rehydration fluids eg lucozade work?
Uptake of Na+ generates an osmotic gradient, and water follows. So the mixture of glucose and salt in the oral rehydration fluid stimulates maximum water uptake.
In what form is protein absorbed into the blood?
As amino acids and small peptides.
How are amino acids transported into enterocytes?
By Na+-amino acid co-transporters. There are different co-transporters for neutral, acidic, basic and imino amino acids.
Most protein products are ingested as dipeptides and tripeptides, not as amino acids. How are dipeptides and tripeptides moved into enterocytes to be converted to amino acids?
Moved by H+ co-transporter - peptide transported 1.
By what enzyme are dipeptides and tripeptides converted into amino acids inside enterocytes?
Cytosolic peptidases.
How is water taken up?
Na+ is moved by active transport out of the enterocyte on the basolateral membrane, and so Na+ diffuses into the enterocytes, taking water with them. Water can then move into the intercellular space and blood. Fluid absorbed is isosmotic.
Both the small and large intestines have Na+/K+ ATPase on the basolateral membrane of the enterocytes. However they transport Na+ differently on their apical membranes. How?
Small intestine - Na+ is co-transported.
Large intestine - Na+ channels, which are induced by aldosterone (more water absorbed to increase BP).
How is calcium absorbed if calcium intake is normal or high?
By passive paracellular absorption.
